Practical considerations aqueous and organic measurements on a single system

Question

Hi all, 
 At our lab we have one 5800 ICP-OES system with an AVS 7 and SPS 4 autosampler. At this moment we are using it to measure aqueous samples, but the plan is to use the same system to develop a method to measure sulfur in biodiesel. 
 I have the kit for semi-volatile solvents on hand. But before i start dismounting i was wondering what would be the most efficient way to allow both aqeous and organic solvents to be measured without having to retube the whole system several times per month. 
 My idea would be to acquire an extra SPS 4 autosampler for the organic solvents. In this case, only the torch/spray chamber/nebulizer and pump tubing need to be replaced when switching methods. Additionally this would allow each method to have it's own rinsing fluids ready to go. 
 I was hoping for some opinions on an efficient, cost effective and low maintenance solution for doing measurements in aqueous and organic matrices on a single ICP-OES system. If there are other important factors to consider, any information is more than welcome! 
 Best regards, 
 Harley

Agilent · Accepted Answer

Hi HarleyD , no worries, we are here to help ! 
 You can definitely work with just one ICP system, I don't see the need to purchase another one for that throughput. If you had dozens or hundreds of organic/aqueous samples per day, then it would be another scenario. One suggestion, if possible, is to organize the samples so that you don't have to prepare the system for each type of sample multiple times a day. For example - you can start the day running organics, then clean the system, run aqueous, clean the system and leave it prepared to the next day. That would have to be aligned with your lab manager to understand the time lost transitioning, and how much that would cost in the end of the day, in terms of throughput. Keep in mind that this is just a suggestion from someone outside of your organization, and maybe you won't have the prediction of your routine. When I worked at a contract lab, we knew what samples we had to do per day, so it was adjusted that way. 
 
 Let me organize the answers here: 
 
 1) My first question would be if the tubing is still useable after dismounting. Of course with proper rinsing, re-fitting relatively new (pump) tubing should not pose a problem. But I do think it could become a likely source of contamination if not done correct and consistently for both methods. Would you suggest to throw away the tubing after switching, regardless of the state of the tubing? 
 A: I would try to keep the tubing if you guarantee that the cleaning is still useful - this might spare a few bucks in a given time. You will be able to see if the tubing is still working seeing some figures of merit of your method (such as %RSD). If they pose a threat to your throughput, then replace them. I would definitely give it a try and re-use them. 
 2) Second question is if all the AVS 7 tubing should be switched out too. I couldn&rsquo;t find a lot of information on this but I assume the tubing going to and from the AVS (incl. sample loop etc.) are useable for both organic and aqueous applications (aqueous currently only uses nitric acid and no HF). Assuming proper rinsing is done between methods of course. I do plan on ordering a small stock of all the non-pump tubing just to be sure. 
 A: I agree with you! They are useable for both applications - but keep in mind what I said before about transitioning from/to organic/aqueous. That is likely to be the most delicate part of the routine. Keeping a small stock of the consumables is the right thing if something goes out of control. 
 3) The extra SPS 4 does have my preference because it saves switching the SPS 4 tubing every time and if necessary having to switch the SPS 4 probe (not sure if this would actually be necessary). Additionally the occurrence of cross-contamination between methods is reduced to only the ICP-OES system. As you said, rinsing the AVS 7 will be an important point in this situation, but I am positive that a good rinsing routine should go a long way. 
 A: Yes, that is correct. The SPS4 for organics usually uses a different probe, but if you are using AVS7, it should be the 1.0mm ID. We recommend the use of MiraMist nebulizer when running AVS7, and you might want to have this one (CP913246, PTFE) that is suitable for both organic and aqueous. Nonetheless, I still recommend a whole sampe intro system for each application. 
 As for the non-ionic detergent, you can go with the Triton X-100 ( https://www.sigmaaldrich.com/BR/en/product/sial/x100 ), diluting it to about 5% m/v. If you see that it is not enough to clean the biodiesel out, try to increase the detergent concentration. But I think that will work just fine. Please note that this link is using my location, but you can use the reference with your local supplier.

Agilent · Answer

Hello HarleyD , 
 That is a great application question. Thanks for sharing with us! 
 AVS apart, you could get an extra SPS4 and a trolley to just switch the sample intro system, depending on how many samples you intend to run. This would speed up your instrument preparation for both organic and aqueous analysis. You still can do it with just one SPS4 (changing tubing and rinse station, or rinsing with proper solvents), but depending on your routine, it would be faster if you have an extra SPS4. 
 If you pretend to use the AVS7 for both applications, then there is something to keep in mind: cleaning the AVS7 with acidic rinse for aqueous applications is quite easy, but organic samples need the proper solvent to ensure that cleaning is successful. In addition, this would prevent any residue from biodiesel to build up in the AVS, avoiding routine problems. Regarding transitions from aqueous/organic and vice versa, you could try a non-ionic detergent solution when finishing the biodiesel routine, before going to aqueous samples, rinsing after that with plenty of acidic solution and water. When going from aqueous to organic, maybe it would be interesting to use butanol or another low-volatile solvent (miscible with biodiesel and with relative solubility in water) to transition from aqueous to organic. Just make sure that the transition solvent you choose will not extinguish the plasma. You still might want to have spare tubings and maybe a rotor seal just in case for the AVS7. 
 Hope this helps you in your demand! 
 Rodolfo

Practical considerations aqueous and organic measurements on a single system

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